1. Field
An aspect according to embodiments of the present invention relates to a pixel and an organic light emitting display device using the same.
2. Description of Related Art
Recently, there have been developed various types of flat panel display devices having reduced weight and volume to address disadvantages of cathode ray tubes. The flat panel display devices include a liquid crystal display device, a field emission display device, a plasma display panel, an organic light emitting display device, and the like.
Among these flat panel display devices, the organic light emitting display device displays images using organic light emitting diodes that emit light through the recombination of electrons and holes.
FIG. 1 is a circuit diagram of a related art pixel of an organic light emitting display device.
Referring to FIG. 1, a pixel 4 of the organic light emitting display device includes an organic light emitting diode (OLED) and a pixel circuit 2 coupled to a data line Dm and a scan line Sn to control the OLED.
An anode electrode of the OLED is coupled to the pixel circuit 2, and a cathode electrode of the OLED is coupled to a second power source ELVSS. The OLED is configured to generate light with a predetermined luminance corresponding to a current supplied from the pixel circuit 2.
When a scan signal is supplied to the scan line Sn, the pixel circuit 2 is configured to control an amount of current supplied to the OLED in response to a data signal supplied to the data line Dm. The pixel circuit 2 includes a second transistor M2″ coupled between a first power source ELVDD and the OLED; a first transistor M1″ coupled between the second transistor M2″ and the data and scan lines Dm and Sn; and a storage capacitor Cst″ coupled between a gate electrode and a first electrode of the second transistor M2″.
A gate electrode of the first transistor M1″ is coupled to the scan line Sn, and a first electrode of the first transistor M1″ is coupled to the data line Dm. A second electrode of the first transistor M1″ is coupled to one terminal of the storage capacitor Cst″. Here, the first electrode is a source electrode or a drain electrode, and the second electrode is the other one of the source and drain electrodes. For example, when the first electrode is the source electrode, the second electrode is the drain electrode, and vice versa. When a scan signal is supplied from the scan line Sn, the first transistor M1″ coupled to the scan and data lines Sn and Dm is turned on in order to supply a data signal supplied from the data line Dm to the storage capacitor Cst″. At this time, a voltage corresponding to a voltage of the data signal is charged into the storage capacitor Cst″.
The gate electrode of the second transistor M2″ is coupled to the one terminal of the storage capacitor Cst″, and the first electrode of the second transistor M2″ is coupled to the other terminal of the storage capacitor Cst″ and the first power source ELVDD. A second electrode of the second transistor M2″ is coupled to an anode electrode of the OLED. The second transistor M2″ controls an amount of current that flows from the first power source ELVDD to a second power source ELVSS via the OLED in accordance with the voltage stored in the storage capacitor Cst″.
However, the pixel 4 of the organic light emitting display device may not display images with uniform luminescence. More specifically, threshold voltages of second transistors M2″, also referred to as drive transistors, included in the respective pixels 4 may be different from one another due to process variations and the like. When the threshold voltages of the drive transistors are different from one another, rays with different luminances are produced by differences in threshold voltages between the drive transistors, although a data signal corresponding to the same gray level is supplied to the plurality of pixels 4.
The organic light emitting display device has a fast response speed and is driven with low power consumption. However, because transistors in the organic light emitting display device may not be uniform, non-uniform pixel luminescence may result. Therefore, research on ways to achieve more uniform luminescence is ongoing.